1. Field of the Invention
The present invention relates to devices for pumping materials and, more particularly, to pumps containing a double-threaded stator accommodating a single-threaded screw-rotor. The device of the present invention can be used for pumping various materials in different branches of industry, including petroleum products, oils, latexes, alkalies, clay solutions and various liquid food products.
2. Description of the Related Art
Known in the art are pumps constructed in accordance with USSR Inv. Cert. No. 1,079,894, 1984, MK F 04 c 5/00, in which an outer threaded surface of a screw-rotor and an internal surface of a stator (conveying tube) are conically shaped. For the purpose of increasing the stability of the pump in the course of operation, the diameter of the threaded surface varies inversely with variations of the external surface diameter.
A disadvantage of this construction is that the coupling of the conical screw-rotor with the stator does not result in maximum specific volume (and, consequently, the capacity) of the area between the rotor threads and the stator.
Also known in the art is a pump constructed in accordance with U.S. Pat. No. 4,406,602, having a parabolic screw. However, a disadvantage of this construction is that the parabolic curve results in a screw geometry that does not maximize the capacity of the pump.
Another known pump is the single-threaded rotary pump II8-OHA manufactured in the USSR. The vertical longitudinal profile of the screw of the II8-OHA represents the reiterative concave and convex catenary lines of arbitrary curvature. When the screw rotates, the material in the closed spaces between the internal and external surfaces of the screw and stator is conveyed by pressure from one closed space to the next over the entire pump length until it reaches the outlet pipe. The screw pump capacity depends on the size of the closed space between the screw and stator surfaces, and the maximum size of the closed space depends on the area defined by the cross-sectional vertical longitudinal profile of the screw.
A disadvantage of a pump constructed in this manner is that, for the given geometry of the screw, the capacity is not maximized since its vertical profile is formed by a catenary line, i.e., by a curve which fails to maximize the use of the area in the screw cross-section.